| Abstract
| - Quantum mechanical calculations have been carried out to investigate the structural properties and the interactionbetween water molecules and silanol groups on the surface of silicalite-1. The (010) surface, which isperpendicular to the straight channel, has been selected and represented by three fragments taken from differentparts of the surface. Calculations have been performed using different levels of accuracy: HF/6-31G(d,p),B3LYP/6-31G(d,p), HF/6-31++G(d,p), and B3LYP/6-31++G(d,p). The basis set superposition error hasbeen taken into account. The geometry of the silanol groups and that of the water molecules have been fullyoptimized. The results show that the most stable conformation takes place when a water molecule forms twohydrogen bonds with two silanols, with only one silanol lying on the opening of the pore of the straightchannel. The corresponding binding energy is −48.82 kJ/mol. These areas are supposed to be the first bindingsites which have to be covered when the water molecule approaches the surface. When the water loadingincreases, the next favorable silanols are those of the opening of the pore in which the four possible complexconformations yield a binding energy between −25.62 and −37.41 kJ/mol. It was also found that the calculatedO−H bond length of the silanol in the free form was slightly shorter than that in the complex. In terms of thestretching frequency, the complexation leads to a red shift of the O−H stretching of the silanol group.
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